The present invention relates generally to a curing oven for adhesive which is cured at an accelerated rate when subjected to ultraviolet radiation. Adhesive is used extensively in many industries as the most efficient means of joining two or more elements, particular for printed circuit boards in the electronics industry. Adhesive is also used in the medical industry, for example, for fabrication of syringes. The inherent disadvantage of the use of adhesive is the time factor for setting or curing the adhesive. This time problem has been solved to a great extent by the use of ultraviolet radiation curing. Ultraviolet radiation curing is a process which involves polymerization, or cross linking of monomers upon exposure of the monomer to ultraviolet radiation. Some monomers do not polymerize when exposed to ultraviolet radiation. For these monomers, a sensitizer is added which absorbs ultraviolet energy, thereby initiating polymerization reaction in the monomer. In addition to a substantial saving of time, there is also a considerable saving in plant space, since an ultraviolet curing line is considerable shorter than previous systems, which for example, utilize gas ovens. Another advantage of ultraviolet curing is that there are no solvents to be discharged into the atmosphere. Since the adhesive polymerizes completely, there is a substantial reduction in air pollution.
One of the most efficient ultraviolet radiation curing systems includes a tubular quartz lamp which includes mercury and argon and produces a high temperature electric arc. A heat sink reflector is positioned above the lamp which reflects the ultraviolet radiation to an area below the lamp where the items to be cured are placed. Cooling systems are provided which work with the heat sink to maintain the lamp at a predetermined temperature for maximum efficiency and to prevent overheating of the lamp to prevent damaging the lamp. One of the major problems of providing a heat sink as part of the cooling system for maintaining the ultraviolet lamp temperature within a predetermined critical range is that the system does not react fast enough to changes in bulb temperature. Heat from the bulb must be absorbed by the heat sink which then must be cooled by the cooling system. This produces wide swings in bulb temperature and a delayed reaction time from adjusting the temperature of the bulb to a predetermined set temperature. In addition to operational problems, the heat sink represents considerable added weight to the curing oven and represents a substantial part of the cost of the oven. The bulb temperature is too critical for direct cooling of the bulb so that the employment of a heat sink system remains the only viable system of the prior art curing ovens.
There are also many safety problems involved with the use of ultraviolet radiation curing systems. The high intensity of the ultraviolet radiation can cause serious burns to the skin and eyes. This problem is complicated by the fact that ultraviolet burns are not felt for several hours, so that serious damage can occur before the individual realizes that damage is occurring. A considerable amount of infrared energy is also produced by the ultraviolet curing system. This also represents a danger to personnel and can damage the products which are being treated by the ultraviolet radiation. Although shields are provided to protect individuals from ultraviolet radiation, a certain amount of radiation still escapes the system. These and other difficulties experienced with the prior art devices have been obviated by the present invention.
It is, therefore, a principle object of the invention to provide an ultraviolet curing system which includes air cooling means which is effective to maintain the ultraviolet bulb temperature within a predetermined temperature range without the use of a heat sink.
Another object of this invention is the provision of a airflow cooling system for an ultraviolet curing oven which creates an induced airflow across the bulb for maintaining the bulb within a predetermined temperature range.
A further object of the present invention is the provision of an ultraviolet curing oven which is readily accessible for insertion of items to be cured and which has automatic safety controls for preventing an individual from being exposed to ultraviolet radiation.
It is a further object of the invention to provide an ultraviolet radiation curing oven which is efficient, easy to operate and is substantially safer to operate than existing systems.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims hereto.